Charged-particle microscopy is a well-known and increasingly important technique for imaging microscopic objects, particularly in the form of electron microscopy. Historically, the basic genus of electron microscope has undergone evolution into a number of well-known apparatus species, such as the Transmission Electron Microscope (TEM), Scanning Electron Microscope (SEM), and Scanning Transmission Electron Microscope (STEM), and also into various sub-species, such as so-called “dual-beam” tools (e.g. a FIB-SEM), which additionally employ a “machining” Focused Ion Beam (FIB), allowing supportive activities such as ion-beam milling or Ion-Beam-Induced Deposition (IBID), for example. More specifically:
In a SEM, irradiation of a specimen by a scanning electron beam precipitates emanation of “auxiliary” radiation from the specimen, in the form of secondary electrons, backscattered electrons, X-rays and photoluminescence (infrared, visible and/or ultraviolet photons), for example; one or more components of this flux of emanating radiation is/are then detected and used for image accumulation purposes, and/or spectroscopic analysis (as in the case of EDX (Energy-Dispersive X-Ray Spectroscopy), for example).
In a TEM, the electron beam used to irradiate the specimen is chosen to be of a high-enough energy to penetrate the specimen (which, to this end, will generally be thinner than in the case of a SEM specimen); the flux of transmitted electrons emanating from the specimen can then be used to create an image, or produce a spectrum (as in the case of EELS (Electron Energy-Loss Spectroscopy), for example). If such a TEM is operated in scanning mode (thus becoming a STEM), the image/spectrum in question will be accumulated during a scanning motion of the irradiating electron beam. More information on some of the topics elucidated here can, for example, be gleaned from the following Wikipedia links:
en.wikipedia.org/wiki/Electron microscope
en.wikipedia.org/wiki/Scanning electron microscope
en.wikipedia.org/wiki/Transmission electron microscopy
en.wikipeda.org/wiki/Scanning transmission electron microscopy
As an alternative to the use of electrons as irradiating beam, charged-particle microscopy can also be performed using other species of charged particle. In this respect, the phrase “charged particle” should be broadly interpreted as encompassing electrons, positive ions (e.g. Ga or He ions), negative ions, protons and positrons, for instance. As regards ion-based microscopy, some further information can, for example, be gleaned from sources such as the following:
en.wikipedia.org/wiki/Scanning Helium Ion Microscope
W. H. Escovitz, T. R. Fox and R. Levi-Setti, Scanning Transmission Ion Microscope with a Field Ion Source, Proc. Nat. Acad. Sci. USA 72(5), pp 1826-1828 (1975).
It should be noted that, in addition to imaging and/or spectroscopy, a charged-particle microscope (CPM) may also have other functionalities, such as examining diffractograms, performing (localized) surface modification (e.g. milling, etching, deposition), etc.
In all cases, a Transmission Charged-Particle Microscope (TCPM) will comprise at least the following components:
A radiation source, such as a Schottky electron source or ion gun.
An illuminator, which serves to manipulate a “raw” radiation beam from the source and perform upon it certain operations such as focusing, aberration mitigation, cropping (with a stop/iris/condensing aperture), filtering, etc. It will generally comprise one or more charged-particle lenses, and may comprise other types of particle-optical component also. If desired, the illuminator can be provided with a deflector system that can be invoked to cause its output beam to perform a scanning motion across the specimen being investigated.
A specimen holder, on which a specimen under investigation can be held and positioned (e.g. tilted, rotated). If desired, this holder can be moved so as to effect a scanning motion of the beam w.r.t. the specimen. In general, such a specimen holder will be connected to a positioning system such as a mechanical stage.
An imaging system, which essentially takes charged particles that are transmitted through a specimen (plane) and directs (focuses) them onto analysis apparatus, such as a detection/imaging device, spectroscopic apparatus, etc. As with the illuminator referred to above, the imaging system may also perform other functions, such as aberration mitigation, cropping, filtering, etc., and it will generally comprise one or more charged-particle lenses and/or other types of particle-optical components.